handoff_not_permitted
This handoff step belongs to someone else: only the recipient accepts, clarifies, declines and reports progress; only the sender answers or re-plans (the fallback owner too once it was declined or went unanswered); a manager may do either.
Problem shape
Every non-2xx response is an RFC 9457 application/problem+json body. The type URI below is stable and machine-matchable, so branch on the final path segment (the code) and treat the status as redundant confirmation. See the error-handling guide.
{
"type": "https://docs.vocapable.com/errors/handoff_not_permitted",
"title": "…",
"status": 403,
"detail": "…",
"instance": "/v1/…"
}